too much gear= bad mpg?

[winkosmosis]

To the guys saying you get good gas mileage with short gears--- remember you have to adjust the mileage the odometer reads.

It doesn't matter if your speedo matches your GPS, the odo is different because it actually comes from the factory with spot on accuracy while the speedo usually reads high.

Drive a known distance and compare that to what the odometer says, then with that ratio you can calculate your real mpg. Or even better, calculate from the stock numbers.

Example: Stock tire size is 28", therefore a 31" tire takes you 1.107 times as far as the odo says. If you changed your gears to 4.56 you divide 3.55/4.56 = you actually drove 0.779 as far as the odo says. Multiply the two 1.107 * 0.779 = 0.86.

So if the odometer says you went 100 miles, you really went 86 miles. How does that affect your gas mileage calculation?

Edit: Simple equation would be (new tire size / stock tire size) * (stock gear / new gear) = actual miles driven per mile the odo reads

 

[winkosmosis]

take two tires, a 215/55/16 and a 33/10.5/15, get em both rolling at 30pmh and let me know which one goes further. thanks try again....

no they run on small tires so the electric engine can turn them in turn not burning fuel for the the good gas milage, but nice try....

and that sucks, guess my jeep wasnt capable, cuz i was getting great gas milage on the freeway(not so much in town)

and im not trying to be a dick, im just tired and in the mood to be a bit facetious is all :thumbup:

There is always some optimal tire size. The XJ's stock tires seem to be optimal, because when people get bigger tires they almost always lose mpg. You're the only person I've heard of who gets better gas mileage with bigger tires.

 

[ktm racer 419]

ON AVERAGE

i get about 2-3 mpg less highway over stock

and 5-6 mpg less city.

i have been able to squeeze out low 20's on occasion though.

i went cross country with adam (93xjli) we calculated our milage using his corrected speedo and my gps, which were always within a couple miles of eachother.

i do not have pixie dust injection in my jeep. when designing vehicles, milage isnt always the top concern. I generally run about 2800 rpm's at 65, and 3000 around 70. I get better milage than one would expect. If i could get rid of much of the added drag and rolling mass I could do a decent amount better. However running those higher rpm's also means more nvh (noise, vibration, harshness). something amc/chrysler wanted to minimize for thier target consumer.

plus, low gears make wheelies easier to do. and wheelies are awesome, and if you don't like wheelies, go buy a prius.

 

[xjtrailrider]

When i figure my mileage I use the odo in the GPS, not the one in the dash. I do get 20 on the highway but in town only around 12-13

 

[MaxxXJ]

When i figure my mileage I use the odo in the GPS, not the one in the dash. I do get 20 on the highway but in town only around 12-13

x2

and when my girl drives my jeep 95% of the time(its her daily driver), the mileage suffers as well cuz she likes the skinny pedal lol

 

[92tahoexj]

To the guys saying you get good gas mileage with short gears--- remember you have to adjust the mileage the odometer reads.

It doesn't matter if your speedo matches your GPS, the odo is different because it actually comes from the factory with spot on accuracy while the speedo usually reads high.

Drive a known distance and compare that to what the odometer says, then with that ratio you can calculate your real mpg. Or even better, calculate from the stock numbers.

Example: Stock tire size is 28", therefore a 31" tire takes you 1.107 times as far as the odo says. If you changed your gears to 4.56 you divide 3.55/4.56 = you actually drove 0.779 as far as the odo says. Multiply the two 1.107 * 0.779 = 0.86.

So if the odometer says you went 100 miles, you really went 86 miles. How does that affect your gas mileage calculation?

Edit: Simple equation would be (new tire size / stock tire size) * (stock gear / new gear) = actual miles driven per mile the odo reads

so, even though you change the speedo gear to compensate for a new gear ratio and tire size, your odometer is still reading the wrong amount of miles driven?

 

[1990heepxj]

take two tires, a 215/55/16 and a 33/10.5/15, get em both rolling at 30pmh and let me know which one goes further. thanks try again....

no they run on small tires so the electric engine can turn them in turn not burning fuel for the the good gas milage, but nice try....

and that sucks, guess my jeep wasnt capable, cuz i was getting great gas milage on the freeway(not so much in town)

and im not trying to be a dick, im just tired and in the mood to be a bit facetious is all :thumbup:

ur logic on this is terrible. if a bigger tire meant better gas milage would a prius not just regear and run 35s like these magical 25 mpg xjs im hearing about? imaging a that gets say 40 mpg, regear it and put 35s on it what happens? 45 mpg? NO, i gaurantee you will get less. put 2 of the same trucks one on 25 inch tires and one on 35 inch tires guess what the one on 35s wont go as far because this idea of lifted trucks losing mpg is nothing new, its just the physics of resistance on a moving object. high way on stock gears u may get a little better mpg with bigger tires and stock gears if u get just the right setting.

 

[in4aride]

ur logic on this is terrible. if a bigger tire meant better gas milage would a prius not just regear and run 35s like these magical 25 mpg xjs im hearing about? imaging a that gets say 40 mpg, regear it and put 35s on it what happens? 45 mpg? NO, i gaurantee you will get less. put 2 of the same trucks one on 25 inch tires and one on 35 inch tires guess what the one on 35s wont go as far because this idea of lifted trucks losing mpg is nothing new, its just the physics of resistance on a moving object. high way on stock gears u may get a little better mpg with bigger tires and stock gears if u get just the right setting.

well like said above, im not using pixie dust, and not the only person out here having experienced this on their XJ's, ive got a few friends on 33's and 35's with stock gears that have seen GREAT milage, ON THE FREEWAY!!!!!!!!!!
at just about 80, i was reading 2100-2200rpm (speedo read considerabbly less, but due to larger diameter and circumfrencei was covering more ground and was actually doing 80)

k here is some thought...

stock tire=28"
28X3.14=87.92" circumfrence, so once rotation stock tire covers 87.92 inches, for ease, lets call this 88"
35X3.14= 109.9" circumfrence, for ease lets call it 110...

so per rotation a 35 will cover an extra 22", almost 2'.

so 22" into 88 puts you at 25%, so per rotation i am going an 25% further than stock.
yes, im a brick floating down the road, you are correct. but once i waste the fule to get it moving, its easier to keep moving.(dont argue, throw 2 bowling balles down the lane at the same speed, whech one is harder to slow down? yes it took more initial energy to get the larger ball up to speed but id love to see you prove it was easier to slow down the heavier ball, its inertia.

im not arguing with you that getting up to speed i get worse gas, i completely agree, around town, milage sucked more than you could imagine, but on the freeway, i got great milage. it breaks down to the fact that for the same rotation of motor/fuel usage, i was covering 25% more ground, how does that equate to worse gas milage?
its not magic its science. i can prove my end, prove me wrong, and no, "well my jeep gets 15 miles to the gallon so youre wrong" doesnt count....

 

[in4aride]

ur logic on this is terrible. if a bigger tire meant better gas milage would a prius not just regear and run 35s like these magical 25 mpg xjs im hearing about? imaging a that gets say 40 mpg, regear it and put 35s on it what happens? 45 mpg? NO, i gaurantee you will get less. put 2 of the same trucks one on 25 inch tires and one on 35 inch tires guess what the one on 35s wont go as far because this idea of lifted trucks losing mpg is nothing new, its just the physics of resistance on a moving object. high way on stock gears u may get a little better mpg with bigger tires and stock gears if u get just the right setting.

and just to piss you off, i had a 2.5L 4door xj on 33's, 5 speed, and stock gears, id get roughly 26-28 mpg on the freeway, super low rpm, for a whole lot of ground covered....

..!....!..

 

[srmitchell]

Ok, now I call B.S.

No way.

 

[in4aride]

Ok, now I call B.S.

No way.

ya i was j/k about the 4 banger, it only got like 15-16mpg lol...i was just trying to get a fired up response lol:greensmok

 

[ktm racer 419]

i dont use fuel injectors

i use magic injectors

 

[techno1154]

well like said above, im not using pixie dust, and not the only person out here having experienced this on their XJ's, ive got a few friends on 33's and 35's with stock gears that have seen GREAT milage, ON THE FREEWAY!!!!!!!!!!
at just about 80, i was reading 2100-2200rpm (speedo read considerabbly less, but due to larger diameter and circumfrencei was covering more ground and was actually doing 80)

k here is some thought...

stock tire=28"
28X3.14=87.92" circumfrence, so once rotation stock tire covers 87.92 inches, for ease, lets call this 88"
35X3.14= 109.9" circumfrence, for ease lets call it 110...

so per rotation a 35 will cover an extra 22", almost 2'.

so 22" into 88 puts you at 25%, so per rotation i am going an 25% further than stock.
yes, im a brick floating down the road, you are correct. but once i waste the fule to get it moving, its easier to keep moving.(dont argue, throw 2 bowling balles down the lane at the same speed, whech one is harder to slow down? yes it took more initial energy to get the larger ball up to speed but id love to see you prove it was easier to slow down the heavier ball, its inertia.

im not arguing with you that getting up to speed i get worse gas, i completely agree, around town, milage sucked more than you could imagine, but on the freeway, i got great milage. it breaks down to the fact that for the same rotation of motor/fuel usage, i was covering 25% more ground, how does that equate to worse gas milage?
its not magic its science. i can prove my end, prove me wrong, and no, "well my jeep gets 15 miles to the gallon so youre wrong" doesnt count....

There is an easy way to verify wether or not larger tires automatically gave better milage.
Take an XJ auto or manual shift is not important.
Fit it with the OEM gears and tire size.
Go to a gas station on a ramp that is close to a highway and fill the gas tank.
Drive for about 100 miles on the highway. Turn around and return to the gas station you last filled the tank.
Fill the tank again at the same station using the same grade of gas. Change the tires for some 33" to 35".
Do the same trip again at the same RPM. Note that I said RPM and not MPH.
Fill the tank again at the same station and compear the difference to fill the tank after each return trip.
Post the results on the forum.

You must drive the same highway in the same direction at the same RPM. The highway you chose to drive is your choice.

I would love to hear of our finding.

 

[in4aride]

at same RPM i am going a faster rate of travel with larger tires, which will NOT get me better gas milage...but i didnt say it would, i said at the speed i traveled the rpms were low enough to get me better gas milage than would be expected...you are taking it into a scenario that is neither what i did nor what i was arguing

 

[Mike H.]

objects in motion want to stay in motion... ???
until there is resistance... and a 35" tire has significant rolling resistance and wind resistance when comaperd to a stockish sized tire.
It will take more power to keep 35" tires turning, which necessitates(sp?) more air/fuel.

 

[in4aride]

I give up. You folks are impossible. Multiple people sayin they have had same results and you guys seem to think it's impossible cuz YOU personally haven't done it. What a joke

 

[XJ=Fun]

Hey guys thanx for the help, now I need help with my actual mpg, i just went through a tank and clocked in at around 300 miles, but i know that this reading is incorrect because of the stock speed. Its a 98 jeep on 4.5 inches of lift at 4.56 and 32x1050x15. how many mpg am i getting?

 

[DeftwillP]

Hey guys thanx for the help, now I need help with my actual mpg, i just went through a tank and clocked in at around 300 miles, but i know that this reading is incorrect because of the stock speed. Its a 98 jeep on 4.5 inches of lift at 4.56 and 32x1050x15. how many mpg am i getting?

Really?? I mean, really? Did you put 15 gallons or 100 gallons in your last tank? I don't know why I ask; doesn't really make much of a difference.

 

[Dest]

5.38's and 35's, aw4. pretty overgeared. governor kicks in at 91 mph.

cruising at 3000 rpms around 70 mph when the jeep is fully loaded i get about 16 mpg.

What governor?

 

[WaXJ_Skier]

What governor?

rev limiter?